The structural and optical properties of the ZnO and Zn_{0.99}O:Eu³⁺ powders synthesized by the hydrothermal method at two different temperatures (150°C and 250°C) were studied. The ZnO and Zn_{0.99}O:0.01Eu³⁺ powders synthesized at 150 and 250°C showed rod- and flower-like morphologies, respectively. The as-synthesized and annealed ZnO and Zn_{0.99}O:0.01Eu³⁺ powders formed the wurtzite crystal structure and P6₃mc space group. The crystallite size of the as-synthesized and annealed ZnO powders increased by the incorporation of Eu³⁺. The photoluminescence properties of annealed Zn_{0.99}O:0.01Eu³⁺ powders were substantially improved by controlling the synthesis temperature. The annealed Zn_{0.99}O:0.01Eu³⁺ powders synthesized at 250°C displayed much stronger emission intensity than those at 150°C.